Articles
Articles are a collaborative effort to provide a single canonical page on all topics relevant to the practice of radiology. As such, articles are written and continuously improved upon by countless contributing members. Our dedicated editors oversee each edit for accuracy and style. Find out more about articles.
716 results found
Article
1.5 T vs 3.0 T
Comparing 1.5 T vs 3.0 T (1.5 tesla vs 3.0 tesla) MRI systems identifies several differences; a 3 T system has
increased signal-to-noise ratio (SNR)
increased spatial resolution
increased temporal resolution
increased specific absorption rate (SAR)
increased acoustic noise
Terminology
It...
Article
3D fast spin echo (MRI sequence)
3D fast spin-echo sequences are MRI pulse sequences that are able to rapidly image relatively large volumes of tissue with high resolution whilst retaining many of the advantages of fast spin-echo sequences.
They are able to create the same weightings as traditional 2D sequences (i.e., T1, T2,...
Article
5 gauss line
The 5 gauss line is the safety line drawn around the perimeter of the main magnet of the MRI scanner, specifying the distance at which the stray magnetic field is equivalent to 5 gauss (0.5 mT).
Five gauss and below are considered 'safe' levels of static magnetic field exposure for the general ...
Article
Abdominal ultrasound
Abdominal ultrasound is a diagnostic imaging technique that evaluates the organs and structures in the abdomen, including the liver, gallbladder, pancreas, spleen, adrenal glands, kidneys, and abdominal aorta.
Normal ultrasound anatomy
On an ultrasound, the normal anatomy of the liver appears ...
Article
Abnormal ductus venosus waveforms
Abnormal ductus venosus waveforms can arise in a number of conditions ranging from aneuploidy to vascular malformations and fetal tumors. "A wave" reversal can be seen in 5% of euploid fetuses 9.
Pathology
Abnormal waveforms in fetal ductus venosus flow assessment can occur in a number of situ...
Article
Absorbed dose
Absorbed dose is a measure of the energy deposited in a medium by ionizing radiation. It is equal to the energy deposited per unit mass of a medium, and so has the unit joules (J) per kilogram (kg), with the adopted name of gray (Gy) where 1 Gy = 1 J.kg-1.
The absorbed dose is not a good indica...
Article
Absorption (ultrasound)
In ultrasound, absorption is the reduction in intensity of the sound waves as it passes through tissue. Most of the energy lost is in the form of heat.
Article
Acoustic enhancement
Acoustic enhancement also called posterior enhancement or enhanced through transmission, refers to the increased echoes deep to structures that transmit sound exceptionally well.
This is characteristic of fluid-filled structures such as cysts, the urinary bladder and the gallbladder. The fluid ...
Article
Acoustic impedance
Acoustic impedance (Z) is a physical property of tissue. It describes how much resistance an ultrasound beam encounters as it passes through a tissue.
Acoustic impedance depends on:
the physical density of the tissue (d, in kg/m3)
the velocity of the soundwave transmitted through the tissue m...
Article
Acoustic shadowing
Acoustic shadowing (sometimes referred to as posterior acoustic shadowing) is a form of ultrasound artifact. It is characterized by the apparent lack of signal deep to an imaged tissue interface, due to all (or nearly all) of the transmitted sound wave being being reflected back to the transduce...
Article
Acquisition time
The time of acquisition for a conventional spin echo or gradient echo sequence is the product of the repetition time, phase encoding steps, and number of averages (TR x phase steps x NEX).
For example, with a one-second TR, 128 phase steps, and two averages, we would get an acquisition time of...
Article
Additive manufacturing
Additive manufacturing is a process, such as stereolithography, in which objects are created by adding layer after layer from the ground up. This process can be contrasted with subtractive manufacturing, a process in which unneeded material is removed to create the desired object in the same way...
Article
Adrenal glands ultrasound
Adrenal glands ultrasound, is an imaging method that can provide valuable information regarding their size, shape, and structure. As a result, it can aid in diagnosing various pathological conditions related to adrenal gland function.
Techniques
Several ultrasound techniques can be employed to...
Article
Advanced multiple beam equalization radiography
The advanced multiple beam equalization radiography (AMBER) system is used to control the distribution of local exposure to the film. An array of independently functioning detectors is used to send feedback signals to the modulators kept in front of the x-ray tube to modulate the exposure levels.
Article
Air bubble artifact
The air bubble artifact on CT is due to the presence of abnormal gas in the oil coolant which surrounds the x-ray tube. The artifact manifests as subtle low density, which has only been described on brain scans.
Cause
The x-ray tube in a CT scanner is prevented from overheating by a heat excha...
Article
Air gap technique
The air gap technique is a radiographic technique that improves image contrast resolution through reducing the amount of scattered radiation that reaches the image detector. In select situations, this technique can be used instead of an antiscatter grid as the primary scatter reduction method in...
Article
Air gap technique (general radiography)
The utilization of the air gap technique in general radiography is limited due to the need for equipment facilitation to create the air gap when it is not inherent in the standard technique.
Horizontal-beam lateral hip
There are many different methods of performing the horizontal beam lateral ...
Article
Air gap technique (mammography)
The air gap technique is utilized for the magnification mammography view.
Magnification mammography is a high dose imaging technique which is generally utilized as a follow-up to a standard mammogram image series when a focal area needs to be more clearly examined 1. The air gap technique is ut...
Article
Aliasing artifact (CT)
Aliasing artifact, otherwise known as undersampling, in CT refers to an error in the accuracy proponent of analog to digital converter (ADC) during image digitization.
Image digitization has three distinct steps: scanning, sampling, and quantization.
When sampling, the brightness of each pix...
Article
Aliasing on MRI
Aliasing on MRI, also known as wrap-around, is a frequently encountered MRI artifact that occurs when the field of view (FOV) is smaller than the body part being imaged. The part of the body that lies beyond the edge of the FOV is projected onto the other side of the image 5.
This can be correc...
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